Triggered Copolypeptide Hydrogel Degradation Using Photolabile Lysine Protecting Groups

We have prepared a new l -lysine-based N -carboxyanhydride monomer containing a photolabile o -nitrobenzyloxycarbonyl protecting group. This monomer was used to prepare poly( l -lysine)- block -poly(oNB- l -lysine) block copolypeptides that formed hydrogels with tunable physical properties and the capability to be degraded by UV irradiation. In these materials, the oNB-lysine residues were found to be excellent surrogates for the hydrophobic residues typically used to form block copolypeptide hydrogels, thus adding functionality without adversely altering self-assembly characteristics. Upon irradiation, full cleavage of the o -nitrobenzyloxycarbonyl groups was observed, resulting in dissolution of the product, poly( l -lysine), and complete hydrogel disruption. When dye molecules were entrapped in the hydrogels, photolysis resulted in release and mixing of these molecules with the surrounding media.